An introducer sheath provides percutaneous access to the vascular system of a patient and functions to permit the introduction and positioning of various minimally invasive medical devices within the patient's vasculature. Minimally invasive medical devices refer to inter alia any type of catheter sized to be introduced into the vasculature to include transcatheter valve prosthesis delivery systems. A conventional introducer sheath includes an elongate tubular component that defines a lumen of the introducer sheath, a hub component, and a hemostasis valve. It is known to commence a minimally invasive procedure within the vasculature by initially forming a percutaneous entry point via the Seldinger technique into a suitable vessel of the patient, such as a femoral, brachial, or radial artery. Thereafter, the elongate tubular component of the introducer sheath is partially inserted into the vasculature at the percutaneous entry point with a proximal port of the introducer sheath hub being accessible by a clinician so that minimally invasive medical devices may be introduced into and advanced through the lumen of the introducer sheath. In many minimally invasive procedures within the vasculature, a guidewire may first be inserted through the introducer sheath and subsequently advanced through the vasculature (and in certain applications another body structure) to a treatment site.
Recently minimally invasive approaches have been developed to facilitate catheter-based implantation of a valve prosthesis on a beating heart that are intended to obviate the need for the use of classical sternotomy and cardiopulmonary bypass. More particularly, flexible prosthetic valves supported by stent structures that can be delivered percutaneously using a catheter-based delivery system have been developed for heart valve replacement, and may be referred to herein as a transcatheter valve or a transcatheter heart valve prosthesis. Transcatheter heart valve prostheses may include either self-expanding or balloon-expandable stent structures with valve leaflets attached to the interior of the stent structure. They are configured to be reduced in diameter, by crimping onto a balloon catheter or by being contained within a sheath or outer tubular component of a delivery catheter, and thereafter advanced through the venous or arterial vasculature. Once the transcatheter heart valve prosthesis is positioned at the treatment site, for instance within an incompetent native valve or a previously implanted prosthetic heart valve, the frame or stent structure may be expanded to hold the prosthetic heart valve firmly in place.
The actual shape or configuration of any particular transcatheter heart valve prosthesis to be delivered in a transcatheter implantation procedure is dependent, at least to some extent, upon the native heart valve being replaced or repaired, i.e., mitral valve, tricuspid valve, aortic valve, or pulmonary valve. Most transcatheter heart valve prosthesis will have a relatively large delivery profile, as will at least a distal portion of a catheter-based delivery system within which the prosthesis is held in a compressed configuration. The use of such larger delivery profile catheter-based delivery systems, heretofore, required a larger diameter or sized introducer sheath in order to provide suitable clearance within the lumen thereof to allow the catheter-based delivery system to pass through the patient's vasculature. However, larger diameter or sized introducer sheaths may be suitable for use only in patients with sufficient vessel size to accommodate such an introducer sheath. In order to extend the availability of larger delivery profile transcatheter heart valve prostheses and their delivery systems to patients with smaller vessel sizes, expandable introducer sheaths with smaller diameters or sizes that are configured to locally expand within the patient's vasculature to allow passage of such prostheses and delivery systems are described in U.S. Patent Application Pub. No. 2014/0121629 to Macaulay et al. and U.S. Patent Application Pub. No. 2014/0236122 to Anderson et al., each of which is incorporated herein by reference in its entirety. Localized radial expansion and subsequent recoil of segments of the expandable introducer sheaths described in the Macaulay and Anderson publications may be less traumatic on the patient's vessel than sustained longitudinal and radial expansion of a fixed, larger diameter introducer sheath.
An expandable introducer sheath must be navigable through the vasculature, and, for certain procedures, it may be necessary for the clinician to accurately steer or deflect the introducer sheath so that a distal port or opening thereof may be aligned with an ostium of a branch or side vessel. It is known to employ a pull wire connected to a distal portion of certain catheters and controlled by a proximal handle component. With such mechanisms, when a wire is pulled, the catheter is deflected in the direction of the pulled wire. However, known pull wire mechanisms are insufficient and inadequate when it comes to accurately and controllably deflecting an expandable introducer sheath due to the longitudinally-extending radially-expandable sections of such introducer sheaths lacking sufficient stiffness or columnar strength to react in a reliable and/or uniform fashion in response thereto.
In light of the above, a need exists for an expandable introducer sheath having a steering mechanism that provides accurate, safe, and predictable deflection of the introducer sheath as it navigates the anatomy of the vasculature.